Plastic screwcap with rotatable washer

ABSTRACT

A plastic screwcap for bottles, of the type relying upon a soft washer or gasket for the actual sealing, the cap being provided with means such as an undercut or a central pin for holding the washer in place on the cap so that it does not adhere to the bottle when it is unscrewed. The arrangement is such that the sealing gasket can rotate freely with the bottle during the last fractional turn while the cap is being tightened, to prevent the sealing washer from being torn at this stage, yet the washer is retained in the cap when the latter is unscrewed instead of adhering to the lip of the bottle which it seals thereby retaining the sealing qualities of the cap for reuse.

Unite ii States :1

Robert J. Williams Dover, Ohio June 19, 1968 Oct. 12, i971 Dover Molded Products Company Dover, Ohio Inventor Appl. No. Filed Patented Assignee References Cited UNITED STATES PATENTS 5/1936 Von Till FOREIGN PATENTS 27,868 6/1964 East Germany 215/40 1,492,276 7/1967 France 215/40 Primary Examiner-George T. Hall Attorney-Max L. Libman ABSTRACT: A plastic screwcap for bottles, of the type relying upon a soft washer or gasket for the actual sealing, the cap being provided with means such as an undercut or a central pin for holding the washer in place on the cap so that it does not adhere to the bottle when it is unscrewed. The arrangement is such that the sealing gasket can rotate freely with the bottle during the last fractional turn while the cap is being tightened, to prevent the sealing washer from being torn at this stage, yet the washer is retained in the cap when the latter is unscrewed instead of adhering to the lip of the bottle which it seals thereby retaining the sealing qualities of the cap for reuse.

PATENTEU um I 2197:

FIG.

FIG. 4..

INVENTOR Robe J. Williams ATTORNEY PLASTIC S ClREWCAlP WITH ROTA'I'ABLIE WASHER BACKGROUND OF THE INVENTION Metal or plastic screwcaps for bottles are in common use, with a disc of soft sealing material, such as cork, paper, felt, or soft plastic to provide the actual sealing closure for the contents of the bottle. In the case of metal caps, it is easy to roll a recess for retaining the sealing washer, but in the art of plastic cap manufacture, the tolerances are such that it is difficult to insure that an undercut molded into the cap will always be of the correct size to properly retain the washer in the cap when the latter is unscrewed by the user. If the washer is made suiticiently large to wedge very tightly into the cap, then due to the softness of the washer material, as the cap is being initially tightened on the bottle, the washer disc being retained on one side by friction against the cap and on the other side by fric tion against the lip of the bottle which is moved relative to the cap, tends to become torn or wrinkled, thus impairing the seal, if not initially, then for further reuse of the cap by the user after the bottle has been initially opened by him. On the other hand, if the washer is too loose in the cap, then it tends to adhere to the lip of the bottle, especially if the contents are somewhat adhesive, as is often the case, and everyone using such bottles has had the experience of the washer adhering fairly tenaciously to the bottle after the cap has been removed, so that in removing it from the bottle, it becomes torn or sufficiently roughened so that it is no longer effective to seal the bottle when the cap is reapplied.

SUMMARY OF THE INVENTION The present invention obviates the above difficulty by providing means for retaining a circular washer disc within a screwcap made of plastic, in such manner that as the cap is tightened on the bottle, the washer disc rotates with the bottle and its opposite surface slides relative to the inside of the cap, so that there is no tendency to tear the washer or sealing disc no matter how firmly the cap is screwed down upon the bottle neck. However, means are also provided which, while permitting suchrotation, retain the washer disc against separation from the cap when the cap is unscrewed from the bottle. This can be accomplished in different ways as will be shown in detail below, one of them being a central pin protruding from the top of the bottle cap through the washer disc, which retains it in place, and another being a series of internal projections or lugs, which together with a small undercut retain the washer in place. In the latter case, a special thread interruption is provided to allow stripping of the cap from the mold without distorting the thread directly below one of such lugs. The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings, in which:

FIG. l is a sectional view taken along line 1-1 of FIG. 2 through a cap embodying the invention;

FIG. 2 is a sectional view taken on line 2-2 of FIG. ll;

FIG. 3 is a longitudinal sectional view taken through a different form of the invention showing the cap prior to application of the sealing gasket;

FIG. d is a view similar to that of FIG. 3 showing the manner in which the sealing gasket is applied to the cap; and

FIG. 5 is a transverse sectional view showing the finished and assembled cap applied to a bottle.

Referring to FIGS. l and 2, the plastic cap 3 is provided with the usual threads 4 for assembling it onto the threaded neck of the bottle or similar container 6. A sealing disc or washer 7 of soft material such as cork, felted paper, plastic, etc., is located under the head 8 of the cap to provide a liquidtight seal as is well known. In most applications, it is desirable to be able to reuse the cap after it has once been opened, and the seal should therefore be of such nature as to make this possible. However, practically every user has had the experience, particularly where the contents of the bottle are somewhat adhesive in nature, of having the sealing disc adhere to the bottle when the cap is unscrew-ed, which is a nuisance in itself even if it can be readily removed and replaced in the cap, but quite often in the process of removing the sealing disc with the finger nails, it is so damaged that it no longer can accomplish the sealing function even if reinserted into the cap. In an effort to minimize this difficulty, the sealing disc is often made larger than the space available in the cap, so that it has to be wedged into position, or else an undercut is provided near the head of the cap to receive the rim of the sealing disc, and thus hold it in place. The difficulty with the first of these expedients is that if the rim of the bottle is at all rough or uneven as is often the case in practice, the last fractional turn of the cap, after contact has been made between the sealing disc and the rim, tends to tear or gouge the material of the sealing disc, or else to wrinkle it, depending upon its thickness and other physical characteristics, so that a satisfactory seal cannot be accomplished. From this point of view, it is more desirable that the sealing disc be able to rotate freely against the head of the cap so that it can be carried along; with the lip of the bottle during the last fractional turn. However, in this case, means must be provided for retaining the sealing disc within the cap so that although it can rotate with the bottle edge as above described, it will not be easily removed from the cap when the cap is unscrewed. In the case of metal caps, which can easily be made to high tolerances due to the nature of the material, it is relatively easy to provide an undercut near the head of the cap so that the sealing disc can be retained therein; in the case of plastic caps, such accuracy is not possible due to the nature of the material and the molding techniques which are employed. It is possible to make only a. very shallow undercut, such as is shown for example at 9 in FIG. 11, since the mold must be withdrawn relative to the cap, this being permitted by the elasticity of the material only to a very limited extent. The combination of the necessarily shallow undercut and the inherently large tolerances required due to the nature of the material have made it impossible to satisfactorily retain the sealing disc 7 with sufficient looseness to pennit it to rotate, and at the same time provide sufficient protrusion of the sealing disc rim into the undercut portion 9 to safely retain the sealing disc.

The present invention overcomes the above problem by providing, in addition to a slight undercut 9, a series of lugs I I shown as four in number, protruding inwardly just below the undercut 9, so that they retain the sealing disc in a positive fashion. The lugs II are sufficiently small to permit safe withdrawal of the mold from the cap interior, except that at one point, where the helical thread 4 terminates near the top of the cap, there may be interference with the mold-stripping operation due to the manner in which the thread approaches at least one of the lugs ill. The difficulty is obviated, in accordance with the present invention, by interrupting the last portion of the internal thread 4 as shown at l3, directly adjacent to that lug which it approaches at that point. By interrupting the thread at this portion, stripping of the cap becomes safely possible without distorting the thread directly below the lug, which would otherwise tend to cause an interference on the fit of the cap to the bottle. While the thread interruption is not necessary in all cases, with the range of hardness required for the present purpose and with the dimensions and configurations needed for the types of bottle caps required, this feature is definitely helpful in reducing cap rejects.

Another arrangement which accomplishes the same result is shown in FIGS. 3-5. In these Figures, the same reference numerals are employed, where applicable, as in FIGS. I and 2, except that a prime is added. In this modification, no undercut is employed, but instead a sharp pin 21 is molded to protrude inwardly from the center of the cap head 3'. In assembling the sealing disc, which may be done either manually or by suitable machinery, the disc 7 is forced down over the pin 21, as shown in FIGS. 1 and 2, and the disc being of soft material is readily penetrated by the pin 21, which is sufficiently long to protrude entirely through the disc as shown in FIG. 4. At this point, the protruding portion of the pin II is headed over, rivet fashion, which may be done manually be touching it with a hot iron, or by heaving a suitably heated or ultrasonic mechanism act upon it, or by cold heading to produce the configuration shown in FIG. 5, whereby a headed rivet is formed, which retains the disc 7 in position, but permits it to rotate about the pin 21 as a pivot when the last fractional turn is given to the cap in order to compress the sealing disc 7 so as to form a tight seal. However, when the cap is unscrewed, the rivet head 21 retains the sealing disc in place, thus accomplishing the same result as in the previous modification.

The underside of the sealing disc 7' is preferably made somewhat rough as shown at to provide good friction with the lip of the bottle, while the other side of the disc is made smooth, so that in contact with the smooth underside of the cap top there is relatively little friction, so that the sealing disc can rotate with respect to the cap and remain stationary with respect to the bottle during the last fractional turn.

I claim:

1. A plastic screwcap for liquid containers, said cap having a cylindrical sidewall and a top head wall,

a. a circular disclike sealing member of soft, deformable material inside of said cap against said head wall,

b. The outer rim of said disclike sealing member fitting sufficiently loosely within said cylindrical sidewall so that the disc can rotate with respect to the cap, when the cap is tightened down on a liquid container, the maximum disc diameter being substantially smaller than the minimum internal diameter of the cylindrical sidewall,

c. and means for obstructing removal of said disc from the cap, said means permitting relative rotation of the cap and sealing disc,

d. said disclike sealing member being smooth on the upper surface,

e. the plastic cap surface which is in contact with said upper surface being also smooth, in the completely closed condition of the cap, to reduce friction between said two surfaces to a minimum.

f. the under surface of the sealing disc, where it engages the lip of a liquid container, being roughened so as to maximize the coefficient of friction between the sealing disc and said lip. 

1. A plastic screwcap for liquid containers, said cap having a cylindrical sidewall and a top head wall, a. a circular disclike sealing member of soft, deformable material inside of said cap against said head wall, b. The outer rim of said disclike sealing member fitting sufficiently loosely within said cylindrical sidewall so that the disc can rotate with respect to the cap, when the cap is tightened down on a liquid container, the maximum disc diameter being substantially smaller than the minimum internal diameter of the cylindrical sidewall, c. and means for obstructing removal of said disc from the cap, said means permitting relative rotation of the cap and sealing disc, d. said disclike sealing member being smooth on the upper surface, e. the plastic cap surface which is in contact with said upper surface being also smooth, in the completely closed condition of the cap, to reduce friction between said two surfaces to a minimum. f. the under surface of the sealing disc, where it engages the lip of a liquid container, being roughened so as to maximize the coefficient of friction between the sealing disc and said lip. 